I`m not Sqad and I`m not an expert but it is possible to suffer dizziness from sinusitis. I think the sinus problem your daughter has is a secondary infection from the flu though. I have had my sinuses x-rayed and I could clearly see the problem on the x-ray. I think if your daughter had a problem it would have been picked up and not missed. My guess would be that the dizziness that she has had from the beginning of the year is caused by something else. The only link that I could imagine regarding the dizziness would be congestion in the ears which could involve the sinuses.